Optionally disable the 304 header due to incompatible aggregators

[jrconlin]

Several popular RSS aggregators (Sage for example) currently don't handle 304's correctly. Instead, they report a URL error and toss out the previously gathered content. I've filed a like bug with that team, but since I have plenty of bandwidth to burn, I've made the 304 report optional:

wp-blog-header.php
Line:136
if (!DISPLAY_OLD_CONTENT) { -- jrc
if ( ($client_last_modified && $client_etag) ?
...
header('HTTP/1.x 304 Not Modified');
exit;
}
}
} Line: 152 --jrc
}

DISPLAY_OLD_CONTENT is defined in wp-config.php so I can re-enable it in the future.

[mdawaffe]

If the client is doing a conditional GET, it needs to understand the response.

Marking as invalid (not a WP problem). Please feel free to discuss.